1. Field of the Invention
This invention pertains to the field of hand tools. More particularly, this invention concerns a spirit-level generally used by carpenters, plumbers and other tradesmen and in particular, concerns a polyfunctional spirit-level that may be used to determine levelness as well as at least two separate degrees of declination.
2. Description of the Prior Art
Spirit-levels are rather well-known in the art, see U.S. Pat. Nos. 1,211,882 and 2,102,364. Generally, they comprise an elongated body wherein is enclosed a short cylindrical transparent sealed tube not quite filled with a slightly viscose liquid so that an air bubble remains entrapped therein. When the tube is aligned axially within the body and the body placed atop a pair of spaced-apart points, the bubble will indicate when the points are parallel with the earth's surface, i.e., "level" by positioning itself midway between the ends of said tube. While some tubes are bowed in the middle, to aid in centering the bubble, others are straight and depend upon surface tension phenomena to aid in centering the bubble. Modernly, short spirit levels having tapered ends are used in the day-to-day activity of many workmen for denoting a level condition, see U.S. Pat. No. 4,419,833. However, in the plumbing trade, there is a need not only to determine the levelness between spaced apart points, but also to determine a minimum degree of declination in a drainage line.
Drainage lines must be sloped downward to provide for gravitational movement of slurried waste material. Construction codes require certain minimum degrees of slope or inclination depending upon the size of the drainage line. For instance, sewage lines three inches or less in diameter must meet the requirement of at least one-fourth inch vertical drop per foot of travel in the direction of flow, whereas sewage lines greater than three inches in diameter must meet a minimum declination of one-eighth inch vertical drop per foot of travel in the direction of flow.
Most sewer lines are installed in ditches that are wet, dirty, cramped and located under pillars, footings, floors and other overhangs. In addition, sewer line pipe is relatively short in length and usually contains at least one belled end so that a continuous sewer line would have periodic interruptions along the outer surface. These conditions make it very difficult to determine whether the sewer line has attained the proper minimum degree of slope. For these reasons, slopes in sewage lines are rarely checked other than by "eye-balling" and this crude method has resulted in inadequate slopes that, in turn, have resulted in many plugged sewer lines. The prior art does teach the use of spirit-levels to determine certain angles such as in railroad tracks, U.S. Pat. No. 487,375, and in ship keels, U.S. Pat. No. 35,298. There is little prior art teaching for the use of spirit-levels to indicate degrees of declination. Thus, there is to date no simple, expedient and easily portable pocket-sized spirit-level for use in determining absolute levelness, two degrees of slope and be useful in a ditch or other confined area generally encountered in certain trades such as the plumbing trade.